Polishing sheet and polishing method

ABSTRACT

Object: To provide a polishing sheet capable of efficiently polishing a hard material such as a metal product so as to form a smooth surface with minimal unevenness. Solution: A polishing sheet (10) including: a substrate (11); a plurality of three-dimensional elements (12) containing abrasive grains and a binding material; and an intermediate layer (13) provided between the three-dimensional elements (12) and the substrate (11) so as to join the substrate (11) and the three-dimensional elements (12), wherein a Youngs modulus of the substrate (11) at 25° C. is not less than 3.0×109Pa; and a Youngs modulus of the intermediate layer (13) at 25° C. is not less than 1.0×107Pa and not greater than 5.0×108Pa.

TECHNICAL FIELD

The present invention relates to a polishing sheet and a polishing method.

BACKGROUND ART

Various polishing materials have been investigated in the past for the purpose of forming smooth surfaces on metal products or the like. For example, Patent Documents 1 and 2 describe a polishing material including a polishing part with a three-dimensional shape.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: H9-502665 T

Patent Document 2: JP 2015-223653 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a polishing sheet capable of efficiently polishing a hard material such as a metal product so as to form a smooth surface with minimal unevenness, and a polishing method capable of efficiently polishing an object to be polished using the polishing sheet.

Means for Solving the Problem

One aspect of the present invention relates to a polishing sheet including: a substrate; a plurality of three-dimensional elements containing abrasive grains and a binding material; and an intermediate layer provided between the three-dimensional elements and the substrate so as to join the substrate and the three-dimensional elements, wherein a Young's modulus of the substrate at 25° C. is not less than 3.0×10⁹ Pa; and a Young's modulus of the intermediate layer at 25° C. is not less than 1.0×10⁷ Pa and not greater than 5.0×10⁸ Pa.

With such a polishing sheet, the unevenness of a target surface can be sufficiently reduced when polishing under a high load. Therefore, with the polishing sheet described above, a hard material such as a metal product can be polished efficiently by high-load polishing, and a smooth surface with minimal unevenness can be formed easily.

Another aspect of the present invention relates to a polishing method including the polishing sheet described above, the method including sliding the polishing sheet and an object to be polished while pressing the polishing sheet against the object to be polished under a load of not less than 1.0×10⁶ Pa.

With such a polishing method, since the polishing sheet described above is used, the object to be polished can be polished efficiently, and a smooth surface with minimal unevenness can be formed easily on the object to be polished.

Yet another aspect of the present invention relates to a polishing sheet including: a substrate; a plurality of three-dimensional elements containing abrasive grains and a binding material; and an intermediate layer provided between the three-dimensional elements and the substrate so as to join the substrate and the three-dimensional elements, wherein the binding material contains a cured product of a resin composition containing an acrylic monomer; and not less than 60 mass % of the acrylic monomer is a polyfunctional monomer selected from the group consisting of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate.

With such a polishing sheet, the unevenness of a surface to be polished can be sufficiently reduced when polishing under a high load. Therefore, with the polishing sheet described above, a hard material such as a metal product can be polished efficiently by high-load polishing, and a smooth surface with minimal unevenness can be formed easily.

Effect of the Invention

An object of the present invention is to provide a polishing sheet capable of efficiently polishing a hard material such as a metal product so as to form a smooth surface with minimal unevenness, and a polishing method capable of efficiently polishing an object to be polished using the polishing sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating one mode of a polishing sheet.

FIG. 2 is a cross-sectional view illustrating another mode of a polishing sheet.

FIG. 3A is a drawing illustrating one mode of the three-dimensional shape of the polishing sheet, and FIG. 3B is a drawing illustrating another mode of the three-dimensional shape of the polishing sheet.

FIG. 4A is a drawing illustrating one mode of the three-dimensional shape of the polishing sheet, and FIG. 4B is a drawing illustrating another mode of the three-dimensional shape of the polishing sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below with reference to the drawings. Note that identical elements are assigned identical codes in the explanation of the drawings, and a duplicate explanation is omitted. Furthermore, the drawings are drawn with a portion embellished in order to ease understanding, and the dimensional ratios and the like are not limited to those shown in the drawings.

Polishing Sheet

The polishing sheet according to this embodiment includes: a substrate; a plurality of three-dimensional elements containing abrasive grains and a binding material; and an intermediate layer provided between the three-dimensional elements and the substrate so as to join the substrate and the three-dimensional elements.

In this embodiment the polishing sheet has the characteristic that (a) the Young's modulus of the substrate at 25° C. is not less than 3.0×10⁹ Pa, and the Young's modulus of the intermediate layer at 25° C. is not less than 1.0×10⁷ Pa and not greater than 5.0×10⁸ Pa; or (b) the binding material contains a cured product of a resin composition containing an acrylic monomer, and not less than 60 mass % of the acrylic monomer is a polyfunctional monomer selected from the group consisting of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate. The polishing sheet may have at least one of the characteristics (a) and (b) and may have both characteristics.

Note that in this specification, tris(2-hydroxyethyl)isocyanurate triacrylate is “(2,4,6-trioxo-1,3,5-triazinane-1,3,5-triyl)triethylene triacrylate”and refers to a compound expressed by the following Formula (A-1). In addition, tris(2-hydroxyethyl)isocyanurate diacrylate is “2-{3-[2-(acryloyloxy)ethyl]-5-(2-hydroxyethyl)-2,4,6-trioxo-1,3,5-triazinan-1-yl}ethyl acrylate” and refers to a compound expressed by the following Formula (A-2).

With the polishing sheet according to this embodiment, the unevenness of a surface to be polished can be sufficiently reduced when polishing under a high load. Therefore, with the polishing sheet described above, a hard material such as a metal product can be polished efficiently by high-load polishing, and a smooth surface with minimal unevenness can be formed easily.

A polishing sheet having the characteristic of (a) described above has a rigid substrate, and therefore the polishing sheet can be slid easily with respect to a fixed hard material, which yields excellent adaptability to high-load polishing. In addition, this polishing sheet is provided with a flexible intermediate layer, and the intermediate layer functions as a buffer layer. Therefore, with the polishing sheet described above, the plurality of three-dimensional elements on the intermediate layer respectively conform to the unevenness of the hard material at the time of high-load polishing, and therefore a smooth surface with minimal unevenness can be formed easily.

Note that in this specification, the Young's modulus of the substrate refers to a value measured by a test related to the tensile properties of a film in accordance with ISO 527-3.

In addition, in this specification, the Young's modulus of the intermediate layer and the Young's modulus of the binding material refers to a complex modulus of elasticity calculated from the results of measuring the dynamic viscoelasticity by means of bending vibration at a frequency of 1 Hz in accordance with ISO 6721-5 under the following conditions.

Measurement Conditions

Measurement device: Solids Analyzer RSA III available from Rheometric Scientific

Measurement mode: Three-point bending

Distance between supports: 40 mm

Frequency: 1 Hz

Rough dimensions of test piece: 10 mm (width)×50 mm (length)×2 mm (thickness)

Strain: 0.05%

In a polishing sheet having the characteristic of (b) described above, the binding material is made of a cured product having a specific isocyanurate structure. Since the compressive yield stress of such a binding material becomes high, the binding material deforms while the pressure applied to the polishing surface is maintained at the time of high-load polishing, and therefore the adhesion to the hard material is enhanced, and high polishing power is achieved. Therefore, with the polishing sheet described above, the unevenness of the target surface can be eliminated easily during high-load polishing, and a smooth surface with minimal unevenness can be formed easily.

Note that in this specification, the compressive yield stress refers to a value obtained by the following measurement method and calculation method.

Measurement Method

A test piece with a rectangular columnar shape is sandwiched between two parallel plate surfaces, and the relationship between the stress and strain at break when a load is applied is determined (in accordance with ISO 604 with the exception of the test piece dimensions and the compressive strain calculation method).

Measurement device: Tensilon universal testing machine (for a 1 KN load cell) available from Orientec

Rate of compression: 1 mm/min

Compressive strain: Nominal compressive strain

Test piece dimensions 2 mm×2 mm×5 mm

Calculation Method

In the compressive stress-strain curve obtained by the measurement method described above, a straight section first appears due to elastic deformation, and a moderate straight portion then appears due to plastic deformation occurring in some sections after an inflection point. The compressive stress value at the intersection of the respective linear regression line formulas of these two straight sections is determined as the compressive yield stress.

A preferred mode of a polishing sheet will be described in detail hereinafter with reference to the drawings.

FIG. 1 is a cross-sectional view illustrating a preferred mode of a polishing sheet. A polishing sheet 10 illustrated in FIG. 1 includes: a substrate 11; three-dimensional elements 12 containing abrasive grains and a binding material; and an intermediate layer 13 disposed between the substrate 11 and the three-dimensional elements 12 so as to join the three-dimensional elements 12 to one side of the substrate 11.

Examples of the substrate 11 include paper substrates, cloth substrates, sponge substrates, resin films, and metal films.

Examples of paper substrates include craft paper, impregnated paper, coated paper, and synthetic paper. In addition, examples of cloth substrates include cotton cloth, rayon cloth, polyester cloth, or a blend thereof Further, examples of sponge substrates include polyurethane foam, polyethylene foam, and melamine foam.

The surface of the substrate 11 in contact with the intermediate layer 13 is preferably smooth, and from the perspective of more easily achieving smoothness and a suitable Young's modulus, the substrate 11 preferably includes a resin film and/or a metal film. Examples of resin films include polyester films, polyimide films, and polyamide films. As a metal film, from the perspective of achieving high thermal conductivity and being able to anticipate frictional heat discharge, a metal foil is preferable, examples of which include aluminum foil and copper foil. The substrate 11 may be a laminate prepared by laminating a plurality of resin films, a laminate prepared by laminating a plurality of metal films, or a laminate including a resin film and a metal film.

The surface of the substrate 11 in contact with the intermediate layer 13 may be subjected to surface treatment for the purpose of enhancing the adhesion with the intermediate layer 13, for example. Examples of this surface treatment include flame treatment, corona treatment, plasma treatment, oxidation treatment with ozone or an oxidizing acid, surface treatment by sputter etching or the like, or primer treatment with a polyethylene acrylic acid, polyurethane, or the like.

The surface of the substrate 11 on the opposite side as the intermediate layer 13 may be surface-treated for the purpose of enhancing adaptability to the polishing device, for example. Examples of this surface treatment include surface roughening treatment by means of sandblasting treatment, the formation of a non-slip layer with an inorganic particle-containing resin, and the provision of an adhesive layer with a pressure-sensitive adhesive.

The thickness of the substrate 11 is not particularly limited and may be, for example, not less than 15 μm and not greater than 60 μm. In addition, the thickness of the substrate 11 may be not greater than 500 μm or not greater than 350 μm. When the thickness of the substrate 11 is large, damage to the substrate is dramatically suppressed at the time of high-load polishing, and the stability of high-load polishing is enhanced. In addition, when the thickness of the substrate 11 is small, conformance to the object to be polished is further enhanced.

The Young's modulus of the substrate 11 at 25° C. is preferably not less than 3.0×10⁹ Pa. Including such a substrate 11 allows the polishing sheet 10 to be slid easily with respect to a fixed hard material, resulting in a polishing sheet 10 having excellent adaptability to high-load polishing.

From the perspective of achieving the aforementioned effect even more prominently, the Young's modulus of the substrate 11 at 25° C. is more preferably not less than 3.5×10⁹ Pa and even more preferably not less than 3.8×10⁹ Pa. Note that when the substrate 11 is a metal film, the Young's modulus of the substrate 11 at 25° C. may be even higher, such as not less than 10×10⁹ Pa or not less than 20×10⁹ Pa, for example.

The upper limit of the Young's modulus of the substrate 11 at 25° C. is not particularly limited. From the perspective of the processability into a rolled product, the Young's modulus of the substrate 11 at 25° C. is preferably not greater than 250×10⁹ Pa and more preferably not greater than 150×10⁹ Pa. Note that when the substrate 11 is a resin film, the Young's modulus of the substrate 11 at 25° C. may be even lower, such as not greater than 20×10⁹ Pa or not greater than 15×10⁹ Pa, for example.

The substrate 11 preferably has a breaking elongation of not greater than 200%. With such a substrate 11, the three-dimensional elements 12 can be fixed more firmly at the time of high-load polishing, and the polishing performance tends to be further enhanced.

From the perspective of achieving the aforementioned effect even more prominently, the breaking elongation of the substrate 11 is more preferably not greater than 180% and even more preferably not greater than 150%. Note that when the substrate 11 is a metal film, the breaking elongation of the substrate 11 may be even lower, such as not greater than 40% or not greater than 30%.

The lower limit of the breaking elongation of the substrate 11 is not particularly limited and may be, for example, not less than 1% or not less than 3%. Note that when the substrate 11 is a resin film, the breaking elongation of the substrate 11 may be even higher, such as not less than 20% or not less than 40%.

The three-dimensional elements 12 contain abrasive grains for polishing the object to be polished and a binding material for binding the abrasive grains. With the three-dimensional elements 12, convex portions that are in contact with the object to be polished and concave portions that are not in contact with the object to be polished are formed on the polishing surface of the polishing sheet 10. That is, the three-dimensional elements 12 on the polishing sheet 10 can be considered elements provided so that the polishing surface has convex portions and concave portions.

The polishing sheet 10 has a plurality of three-dimensional elements 12, and the three-dimensional elements 12 are independent of one another. Employing such a configuration allows the plurality of three-dimensional elements 12 to respectively conform to the unevenness of the object to be polished at the time of high-load polishing.

The abrasive grains may be selected appropriately in accordance with the application of the polishing sheet 10 (for example, the type of the object to be polished, or the type of the polishing device to which the polishing sheet is applied). Examples of abrasive grains include diamond, fused aluminum oxide, heat-treated aluminum oxide, ceramic aluminum oxide, silicone carbide, alumina zirconia, garnet, and cubic boron nitride. One type of these may be used alone, or two or more types may be used as a mixture, and they may also be processed into a concentrated abrasive grain shape. Of these, diamond, silicone carbide, and cubic boron nitride are particularly preferable in that the suitability for high-load polishing of a solid material is high.

The average particle size of the abrasive grains may be selected appropriately in accordance with the application of the polishing sheet 10. The average particle size of the abrasive grains may be, for example, not less than 0.3 μm, and is preferably not less than 0.5 μm and more preferably not less than 10 μm. In addition, the average particle size of the abrasive grains may be, for example, not greater than 50 μm, and is preferably not greater than 35 μm and more preferably not greater than 20 μm. Further, when the abrasive grains are concentrated, the average particle size thereof may be, for example, not less than 5 μm, and is preferably not less than 10 μm and more preferably not less than 20 μm. In addition, the average particle size of concentrated abrasive grains may be, for example, not greater than 5 mm, and is preferably not greater than 1 mm and more preferably not greater than 500 μm.

Note that in this specification, the average particle size of polishing particles is the volume cumulative size D50 measured using laser diffraction/scattering type particle size distribution measurements. The specific measurement conditions are as follows, but there is no problem with using other measurement devices and conditions as long as it can be understood by a person skilled in the art that equivalent values are obtained based on the same principle.

Measurement device: LA-920 Laser diffraction/scattering type particle size distribution measurement device (Horiba, Ltd., Kyoto-shi, Kyoto)

Analytical software: LA-920 for Windows (trade name)

Abrasive grain amount: 150 mg

Dispersion medium: 150 mL of ion-exchanged water

Circulation rate (water stirring rate): Preset value of 15

Ultrasonic oscillation: Yes (using ultrasonic device built into LA-920)

Measurement temperature: Room temperature (25° C.)

Relative humidity: Not higher than 85%

He—Ne laser beam transmittance: 85%

Tungsten lamp transmittance: 85%

Relative refractive index: Set to 1.80 (relative refractive index of diamond: 1.81)

Measurement time: 20 sec

Number of data fetches: 10

Particle size basis: Volume

The yarn count of the abrasive grains, which is defined by JIS R-6001-2:2017, may be, for example, from #280 to #30000 and is preferably from #600 to #20000.

The content of abrasive grains in the three-dimensional elements 12 may be, for example, not less than 0.2 parts by mass and is preferably not less than 0.4 parts by mass and more preferably not less than 1 part by mass per 100 parts by mass of the binding material. In addition, the content of abrasive grains in the three-dimensional elements 12 may be, for example, not greater than 800 parts by mass and is preferably not greater than 600 parts by mass and more preferably not greater than 500 parts by mass per 100 parts by mass of the binding material.

The binding material may be considered a matrix for dispersing the abrasive grains. The binding material may be, for example, a cured product of a thermosetting resin composition or a cured product of a photocurable resin composition.

The Young's modulus of the binding material at 25° C. is preferably not less than 1.0×10⁹ Pa. With such a binding material, the shape of the three-dimensional elements 12 can be sufficiently maintained even under a high load, and the polishing power with respect to the object to be polished tends to be expressed more prominently.

From the perspective of achieving the aforementioned effect even more prominently, the Young's modulus of the binding material at 25° C. is more preferably not less than 2.0×10⁹ Pa and even more preferably not less than 4.0×10⁹ Pa. The upper limit of the Young's modulus of the binding material at 25° C. is not particularly limited and may be, for example, not greater than 20×10⁹ Pa or not greater than 15×10⁹ Pa.

In a preferred aspect, the binding material may contain a phenol resin. Such a binding material easily yields the preferred Young's modulus described below.

In another preferred mode, the binding material may be a cured product of a resin composition containing an acrylic monomer. An acrylic monomer is a compound having at least one type of polymerizable group selected from the group consisting of acryloyl groups and methacryloyl groups. The resin composition is cured by the polymerization of the acrylic monomer to form a cured product constituting the binding material.

Not less than 60 mass % of the acrylic monomer of the resin composition may be a polyfunctional monomer selected from the group consisting of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate. As a result, since a binding material with high compressive yield stress is formed, the binding material can be deformed while maintaining the pressure applied to the polishing surface at the time of high-load polishing. Thus, the adhesion to the hard material is enhanced, and high polishing power can be achieved.

The content of the polyfunctional monomer in the acrylic monomer is preferably not less than 65 mass % and preferably not less than 85 mass %, and the content may be not less than 95 mass %, not less than 99 mass %, or not less than 100 mass %.

The resin composition may further contain acrylic monomers other than the polyfunctional monomer described above. A monomer having a glass transition temperature of not lower than 25° C. in the form of a single polymer is preferable as another acrylic monomer. As other acrylic monomers, examples of monofunctional monomers include isobornyl(meth)acrylate, dicyclopentanyl(meth)acrylate, and dicyclopentenyl(meth)acrylate; examples of difunctional monomers include tricyclodecanemethanol di(meth)acrylate and bisphenol A ethylene oxide-modified di(meth)acrylate; and examples of polyfunctional monomers include trimethylpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, ditrimethylolpropane, tetracrylate, dipentaerythritol pentacrylate, dipentaerythritol hexacrylate, and ε-caprolactone-modified tris-(2-acryloxyethyl)isocyanurate.

The content of the acrylic monomer in the resin composition may be, for example, not less than 90 mass % and is preferably not less than 95 mass % and more preferably not less than 99 mass % on the basis of the total amount of solid content in the resin composition. The upper limit of the content of the acrylic monomer in the resin composition is not particularly limited.

The resin composition may further contain a polymerization initiator for initiating the polymerization of the acrylic monomer. Examples of polymerization initiators include heat polymerization initiators and photopolymerization initiators. Of these, a photopolymerization initiator for initiating free radical polymerization is preferable. Examples of intramolecular cleavage type photopolymerization initiators include benzoin derivatives, benzyl ketal, α-hydroxyacetophenone, α-aminoacetophenone, acyl phosphine oxides, titanocenes, and O-acyloximes, and examples of hydrogen abstraction type photopolymerization initiators include benzophenone, Michler's ketone, and thioxanthone.

The content of the polymerization initiator in the resin composition may be modified appropriately in accordance with the type of the polymerization initiator or the like. The content of the polymerization initiator in the resin composition may be, for example, not less than 0.1 parts by mass and is preferably not less than 0.5 parts by mass and more preferably not less than 1.0 parts by mass per 100 parts by mass of the acrylic monomer. In addition, the content of the polymerization initiator in the resin composition may be, for example, not greater than 10 parts by mass and is preferably not greater than 5 parts by mass and more preferably not greater than 3 parts by mass per 100 parts by mass of the acrylic monomer.

The resin composition may further contain components other than an acrylic monomer and a polymerization initiator. Examples of the components include coupling agents, wetting agents, dyes, pigments, plasticizers, fillers, release agents, polishing aids, and other additives.

In FIG. 1, the three-dimensional elements 12 are illustrated with a shape in which the cross section forms a triangular shape, but the shape of the three-dimensional elements 12 is not necessarily limited to this example. The three-dimensional elements 12 may, for example, have a conical structure which has a convex portion as a vertex and is joined with the intermediate layer 13 on the bottom surface. In addition, the three-dimensional elements 12 may, for example, have a triangular prism which forms a convex portion on one edge and is joined with the intermediate layer 13 on the side surface opposite this edge.

Further, the three-dimensional elements 12 may, for example, have a columnar structure which forms a convex portion with one base surface and is joined with the intermediate layer 13 on the other base surface. In addition, the three-dimensional elements 12 may, for example, have a frustum structure which forms a convex portion with one base surface and is joined with the intermediate layer 13 on the other base surface.

The three-dimensional elements 12 may also have a multilayer structure. For example, the three-dimensional elements 12 may be formed from a polishing material layer made of abrasive grains and a binding material and a support layer made of a binding material.

The height of the three-dimensional elements 12 (height from a concave portion to a convex portion of the polishing surface) may be, for example, from 2 to 800 μm or from 4 to 400 μm.

The intermediate layer 13 is a layer which is disposed between the substrate 11 and the three-dimensional elements 12 so as to join the substrate 11 and the three-dimensional elements 12.

The Young's modulus of the intermediate layer 13 at 25° C. is preferably not less than 1.0×10⁷ Pa. With such an intermediate layer 13, the three-dimensional elements 12 can be sufficiently fixed to the substrate 11, and therefore the shedding or the like of the three-dimensional elements 12 at the time of polishing can be sufficiently suppressed.

From the perspective of achieving the aforementioned effect even more prominently, the Young's modulus of the intermediate layer 13 at 25° C. is more preferably not less than 3.0×10⁷ Pa and even more preferably not less than 5.0×10⁷ Pa.

In addition, the Young's modulus of the intermediate layer 13 at 25° C. is preferably not greater than 5.0×10⁸ Pa. Such an intermediate layer 13 functions as a buffer layer at the time of high-load polishing and enables the plurality of three-dimensional elements 12 to respectively conform to the unevenness of the object to be polished. Therefore, with such an intermediate layer 13, a smooth surface with minimal unevenness can be formed easily.

From the perspective of achieving the aforementioned effect even more prominently, the Young's modulus of the intermediate layer 13 at 25° C. is more preferably not greater than 4.0×10⁸ Pa and even more preferably not greater than 2.0×10⁸ Pa.

The constituent material of the intermediate layer 13 is not particularly limited as long as it can join the substrate 11 and the three-dimensional elements 12. The intermediate layer 13 may, for example, be made of a cured product of a thermosetting resin composition or a cured product of a photocurable resin composition.

In one preferred mode, the intermediate layer 13 may be made of a cured product of a resin composition containing a urethane acrylate. Such an intermediate layer 13 tends to easily achieve both the preferred Young's modulus described above and strong adhesive strength between the substrate 11 and the three-dimensional elements 12.

A urethane acrylate can be considered a polymerizable compound containing a urethane bond and at least one type of polymerizable group selected from the group consisting of an acryloyl group and a methacryloyl group. Specific examples of urethane acrylates include polyester skeleton-containing urethane acrylates, polyether skeleton-containing urethane acrylates, aliphatic urethane acrylates, and aromatic urethane acrylates.

The resin composition may further contain polymerizable compounds other than urethane acrylates. The polymerizable compounds may be selected appropriately from compounds that are copolymerizable with urethane acrylates. Examples of the polymerizable compounds include tetrahydrofurfuryl(meth)acrylates, 2-phenoxyethyl(meth)acrylates, benzyl(meth)acrylates, cyclic trimethylolpropane formal acrylates, glycidyl methacrylates, and (meth)acrylic acids. In addition, the resin composition may further contain polymerizable compounds that do not copolymerize with urethane acrylates such as epoxy resins.

The proportion of urethane acrylates constituting the polymerizable compound in the resin composition may be, for example, not less than 40 mass % and is preferably not less than 50 mass % and more preferably not less than 70 mass %. As a result, the preferred Young's modulus described above is more easily achieved.

The upper limit of the proportion of urethane acrylates constituting the polymerizable compound in the resin composition is not particularly limited and may be, for example, not greater than 99.9 mass % or not greater than 99 mass %.

The resin composition may further contain a polymerization initiator for initiating the polymerization of the urethane acrylate. Examples of polymerization initiators include heat polymerization initiators and photopolymerization initiators. Of these, a photopolymerization initiator for initiating free radical polymerization is preferable. Examples of intramolecular cleavage type photopolymerization initiators include benzoin derivatives, benzyl ketal, α-hydroxyacetophenone, α-aminoacetophenone, acyl phosphine oxides, titanocenes, and O-acyloximes, and examples of hydrogen abstraction type photopolymerization initiators include benzophenone, Michler's ketone, and thioxanthone.

The content of the polymerization initiator in the resin composition may be modified appropriately in accordance with the type of the polymerization initiator or the like. The content of the polymerization initiator in the resin composition may be, for example, not less than 0.1 parts by mass and is preferably not less than 0.5 parts by mass and more preferably not less than 1.0 parts by mass per 100 parts by mass of the polymerizable compound. In addition, the content of the polymerization initiator in the resin composition may be, for example, not greater than 50 parts by mass and is preferably not greater than 20 parts by mass and more preferably not greater than 10 parts by mass per 100 parts by mass of the polymerizable compound.

The resin composition may further contain components other than a polymerizable compound and a curing agent. Examples of the components include coupling agents, wetting agents, dyes, pigments, plasticizers, fillers, and other additives.

In the polishing sheet 10, the intermediate layer 13 is molded three-dimensionally together with the three-dimensional elements 12 so as to form concave portions in the polishing surface. In addition, the polishing sheet 10 has a plurality of intermediate layers 13, and the plurality of intermediate layers 13 respectively join one three-dimensional element 12 and the substrate 11. That is, in the polishing sheet 10, one three-dimensional element 12 is provided on one intermediate layer 13.

In this embodiment, the shape of the intermediate layers is not limited to the shape described above. For example, a plurality of three-dimensional elements may be joined with the substrate by a single intermediate layer. In other words, a plurality of three-dimensional elements may be provided on a single intermediate layer.

FIG. 2 is a cross-sectional view illustrating another mode of a polishing sheet. A polishing sheet 20 illustrated in FIG. 2 includes a substrate 21, a plurality of three-dimensional elements 22, an intermediate layer 23 disposed between the substrate 21, and the three-dimensional elements 22 so as to join the substrate 21 and the plurality of three-dimensional elements. The intermediate layer 23 is joined with the substrate 21 on one side and is joined with the plurality of three-dimensional elements 22 on the other side. The surface of the intermediate layer 23 on the side that is in contact with the three-dimensional elements 22 is molded three-dimensionally together with the three-dimensional elements 22 so as to form concave portions in the polishing surface.

The substrate 21 and the three-dimensional elements 22 may be the same as the substrate 11 and the three-dimensional elements 12 of the polishing sheet 10, and the intermediate layer 23 may be the same as the intermediate layer 13 of the polishing sheet 10 with the exception of the shape thereof.

Note that the intermediate layer 23 is molded three-dimensionally together with the three-dimensional elements 22 so as to form a three-dimensional shape on the polishing surface, but the intermediate layer 23 does not necessarily need to be molded three-dimensionally, and the three-dimensional elements 22 may also be provided on a smooth surface of the intermediate layer 23.

In this embodiment, a three-dimensional shape is formed by the three-dimensional elements (the three-dimensional elements and the intermediate layer in some cases) on the polishing surface of the polishing sheet. A preferred mode of this three-dimensional shape will be illustrated hereinafter with reference to the drawings.

FIG. 3A is a top view illustrating one mode of the three-dimensional shape of the polishing sheet. A three-dimensional part 121 has a conical structure (trigonal pyramid structure) which has a vertex forming a convex portion and is joined to the substrate side on the bottom surface. Note that in FIG. 3A, a plurality of three-dimensional parts 121 make contact with one another on the bottom edges of the pyramid structure, but the plurality of three-dimensional parts 121 may also be separated from one another.

In FIG. 3A, symbol o indicates the bottom edge length of the three-dimensional part 121, and symbol p indicates the distance between the vertices of adjacent three-dimensional parts 121. Here, o may be, for example, from 5 μm to 1000 μm and is preferably from 10 μm to 500 μm. In addition, p may be, for example, from 5 μm to 1000 μm or from 10 μm to 500 μm.

FIG. 3B is a top view illustrating another mode of the three-dimensional shape of the polishing sheet. A three-dimensional part 122 has a frustum structure which forms a convex portion with one base surface and is joined to the substrate side on the other base surface. In FIG. 3B, a plurality of three-dimensional parts 122 are separated from one another, but the plurality of three-dimensional parts 122 may also make contact with one another on the bottom edges on the substrate side.

In FIG. 3B, symbol o indicates the bottom edge length on the substrate side of the three-dimensional part 122, symbol u indicates the distance between the bottom edges of adjacent three-dimensional parts 122, and symbol y indicates the length of the bottom edge of the three-dimensional part 122 on the side forming the convex portion. Here, o may be, for example, from 5 am to 2000 μm and is preferably from 10 μm to 1000 μm. In addition, u may be, for example, from 0 to 1000 μm and is preferably from 2 μm to 500 μm. Further, y may be, for example, from 0.5 μm to 1,800 μm and is preferably from 1 μm to 900 μm.

FIG. 4A is a cross-sectional perspective view illustrating another mode of the three-dimensional shape of the polishing sheet. A three-dimensional part 123 has a triangular prism structure which forms a convex portion on one edge and is joined with the substrate side on the side surface opposite this edge. The three-dimensional part 123 has a multilayer structure including three-dimensional elements 132 and intermediate layers 133.

Note that in FIG. 4A, three-dimensional elements having a triangular prism structure and a multilayer structure are illustrated, but the three-dimensional part having a triangular prism structure may also be formed from only three-dimensional elements without having a multilayer structure.

The vertical angle a of the three-dimensional part 123 may be, for example, from 30° to 150° or from 45° to 140° . In FIG. 4A, symbol h indicates the height of the three-dimensional part 123, and symbol s indicates the height of the three-dimensional element 132. Here, h may be, for example, from 10 μm to 10000 μm and is preferably from 20 μm to 1000 μm. In addition, s may be, for example, from 5% to 95% and is preferably from 10% to 90% of the height h of the three-dimensional part.

In FIG. 4A, symbol w indicates the length of the short base edge of the three-dimensional part 123 (width of the three-dimensional part 123), symbol p indicates the distance between the vertices of the three-dimensional parts 123, and symbol u indicates the distance between the long base edges of adjacent three-dimensional parts 123. Here, w may be, for example, from 2 μm to 2000 μm and is preferably from 4 μm to 1000 μm. In addition, p may be, for example, from 2 μm to 4000 μm and is preferably from 4 μm to 2000 μm. Further, u may be, for example, from 0 to 2000 μm and is preferably from 0 to 1000 μm.

The length of the three-dimensional part 123 (length of the long base edge) may be extended along the entire length of the polishing sheet. In this case, both ends in the long base edge direction of the three-dimensional part 123 are near the ends of the polishing sheet, and a plurality of three-dimensional parts 123 are disposed in a striped pattern.

In addition, the length of the long base edge of the three-dimensional part 123 may be set to an appropriate length such as from 5 μm to 10000 μm, for example. An example of this case is illustrated in FIG. 4B. In FIG. 4B, the end face of a three-dimensional part 124 assumes a shape which is cut out at an acute angle from below, but the end face of the three-dimensional part 124 is not limited to such a shape.

In FIG. 4B, symbol l indicates the length of the long base edge of the three-dimensional part 124, and symbol x indicates the distance between the short base edges of adjacent three-dimensional parts 124. Here, l may be, for example, from 5 μm to 10000 μm and is preferably from 10 μm to 5000 μm. Further, x may be, for example, from 0 to 2000 μm and is preferably from 0 to 1000 μm.

With the polishing sheet according to this embodiment, the unevenness of a surface to be polished can be sufficiently reduced when polishing under a high load. Therefore, the polishing sheet described above can be suitably used in applications for high-load polishing. That is, the polishing sheet may be a polishing sheet for high-load polishing.

The load during high-load polishing may be, for example, not less than 1.0×10⁶ Pa and is preferably not less than 1.2×10⁶ Pa and even more preferably not less than 1.5×10⁶ Pa. In addition, the load during high-load polishing may be, for example, not greater than 5.0×10⁶ Pa and is preferably not greater than 3.0×10⁶ Pa.

Further, since the polishing sheet described above is suitable for high-load polishing, it can be suitably used in polishing applications for hard materials such as metal products. That is, the polishing sheet may be a polishing sheet for hard material polishing.

A hard material refers to a material in which the Vickers hardness defined by ISO 8486-2:2007, for example, is not less than HV150. Examples of hard materials include carbon steel, stainless steel, titanium, tungsten, and ceramic materials such as silicon carbide, aluminum nitride, zirconia, and alumina.

Polishing Method

The polishing method according to this embodiment includes sliding the polishing sheet and an object to be polished while pressing the polishing sheet against the object to be polished.

In this embodiment, the load when pressing the polishing sheet against the object to be polished may be, for example, not less than 1.0×10⁶ Pa. This load is, for example, preferably not less than 1.2×10⁶ Pa and even more preferably not less than 1.5×10⁶ Pa. The upper limit of this load may be, for example, not greater than 5.0×10⁶ Pa and is preferably not greater than 3.0×10⁶ Pa.

The sliding of the polishing sheet and the object to be polished may be achieved by fixing one and sliding the other or by sliding both members. In this embodiment, the method of fixing the object to be polished and sliding the polishing sheet is particularly preferable among these methods.

The object to be polished is not particularly limited but is preferably the hard material described above from the perspective of prominently achieving the effects of using the polishing sheet described above.

In this embodiment, a lubricating liquid may be interposed when sliding the polishing sheet and the object to be polished. Lubricating liquids are broadly divided into water-soluble and non-water-soluble liquids. Water-soluble lubricating liquids include soluble type, solution type, and emulsion type liquids, and any of these may be used. In addition, examples of non-water-soluble lubricating liquids include lubricating liquids made of mineral oils and/or fatty oils, and these lubricating liquids may or may not contain extreme-pressure additives.

Although descriptions were given above for the preferred embodiments of the present invention, the present invention is not limited to the aforementioned embodiments.

EXAMPLES

The present invention will be described more specifically below using examples, but the present invention is not intended to be limited to the examples.

Example A-1

Preparation of Composition (a-1) for Three-Dimensional Element Formation

A composition (a-1) for three-dimensional element formation was prepared using PR-53074 (liquid resol type phenol resin: available from Sumitomo Bakelite Co., Ltd., non-volatile content: 75%) as a phenol resin.

Specifically, a first mixture was obtained by mixing 140 parts by mass of PR-53074, 17.5 parts by mass of propylene glycol methyl ether, and 17.5 parts by mass of propylene glycol methyl ether acetate. Next, a second mixture was obtained by mixing 300 parts by mass of diamond abrasive grains (average particle size: 15 μm) and 200 parts by mass of isopropyl alcohol. A composition (a-1) for three-dimensional element formation was prepared by mixing the first mixture and the second mixture.

Composition (b-1) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared using CN991 (available from Arkema (Colombes Cedex, France)) as a urethane acrylate.

Specifically, the composition (b-1) for intermediate layer formation was prepared by mixing 78.43 parts by mass of CN991, 19.61 parts by mass of tetrahydrofurfuryl acrylate, and 1.96 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins (Waalmijk, The Netherlands)).

Substrate

A PET film (thickness: 75 μm, Young's modulus at 25° C.: 4×10⁹ Pa) was prepared as a substrate.

Production of Polishing Sheet

A polypropylene molded sheet having concave portions corresponding to the three-dimensional shape illustrated in FIG. 3A was prepared. The composition (a-1) for three-dimensional element formation was applied to the top of the molded film with a bar coater, and the concave portions of the molded film were filled with the composition (a-1) and dried for 3 minutes at 75° C.

Next, the composition (b-1) for intermediate layer formation was applied to the top of the molded film, and a transparent polyester film with a thickness of 75 μm was layered as a substrate and laminated by applying pressure with a roller. Ultraviolet rays were irradiated from the polyester film side, and the film was then heated for 24 hours at 90° C.

The molded film was peeled off and additionally heated for 24 hours at 110° C. to obtain a polishing sheet.

Example A-2

Composition (b-2) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared using CN991 (Arkema) as a urethane acrylate and YDCN-700-10 (cresol novolac type epoxy resin, available from Nippon Steel & Sumikin Chemical Co., Ltd. (Chiyoda-ku, Tokyo) as an epoxy resin.

Specifically, the composition (b-2) for intermediate layer formation was prepared by mixing 56.49 parts by mass of CN991, 18.83 parts by mass of tetrahydrofurfuryl acrylate, 4.01 parts by mass of isobornyl acrylate, 15.06 parts by mass of YDCN-700-10, 1.60 parts by mass of a photopolymerization initiator (Omnirad 907, available from IGM Resins), and 4.01 parts by mass of an epoxy resin curing agent (2-ethyl-4-ethylimidazole).

Production of polishing sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (b-2) for intermediate layer formation was used instead of the composition (b-1) for intermediate layer formation.

Example A-3

Composition (b-3) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared using CN991 (available from Arkema) as a urethane acrylate.

Specifically, the composition (b-3) for intermediate layer formation was prepared by mixing 73.17 parts by mass of CN991, 24.39 parts by mass of cyclic trimethylolpropane formal acetate, and 2.44 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins).

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (b-3) for intermediate layer formation was used instead of the composition (b-1) for intermediate layer formation.

Example A-4

Preparation of Composition (a-2) for Three-Dimensional Element Formation

A composition (a-2) for three-dimensional element formation was prepared in the same manner as in Example A-1 with the exception that diamond abrasive grains with an average particle size of 20 μm were used as diamond abrasive grains.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (a-2) for three-dimensional element formation was used instead of the composition (a-1) for three-dimensional element formation.

Comparative Example X-1

Composition (b-4) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared without using a urethane acrylate.

Specifically, the composition (b-4) for intermediate layer formation was prepared by mixing 36.55 parts by mass of isobornyl acrylate, 21.69 parts by mass of trimethylolpropane triacrylate (SR351S, available from Arkema), 36.15 parts by mass of YDCN-700-10, 1.60 parts by mass of a photopolymerization initiator (Omnirad 907, available from IGM Resins), and 4.01 parts by mass of an epoxy resin curing agent (2-ethyl-4-ethylimidazole).

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (b-4) for intermediate layer formation was used instead of the composition (b-1) for intermediate layer formation.

Comparative Example X-2

Composition (b-5) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared using CN991 (available from Arkema) as a urethane acrylate.

Specifically, the composition (b-5) for intermediate layer formation was prepared by mixing 48.78 parts by mass of CN991, 16.26 parts by mass of cyclic trimethylolpropane formal acetate, 32.52 parts by mass of SR368D (mixture of trimethylolpropane triacrylate:tris(2-hydroxyethyl)isocyanurate triacrylate=70:30 (mass ratio), available from Arkema), and 2.44 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins).

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (b-5) for intermediate layer formation was used instead of the composition (b-1) for intermediate layer formation.

Comparative Example X-3 Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example A-1 with the exception that the composition (a-2) for three-dimensional element formation was used instead of the composition (a-1) for three-dimensional element formation and that the composition (b-4) for intermediate layer formation was used instead of the composition (b-1) for intermediate layer formation.

Polishing Sheet Evaluation (1)

The polishing sheets produced in the examples and the comparative examples were subjected to polishing tests under the following conditions (1), and the cut amount and the surface roughness Ra of the polished surface after 60 seconds were determined. The results are shown in Tables 1 and 2.

Polishing Test Conditions (1)

Polished object: S45C (not heat-treated)

Polished object size: 10 mm (Φ)×150 mm (length)

Polishing device: Super Finisher (available from Matsuda Seiki Co., Ltd.)

Revolution speed: 825 rpm

Film feeding: none

Oscillation speed: 1000 rpm

Grinding fluid: 2% aqueous solution of Cimtech 500 (available from CIMCOOL FLUIDS TECHNOLOGY)

Backup roller hardness: Shore A 30°

Notch depth: 4.2 mm

Polishing time: 60 sec

Cut amount: The reduction in the weight of the object to be polished after the polishing test was used as the cut amount.

Average surface roughness Ra: Measured with the following device/conditions.

Device: SURFTEST SV-3100H4 available from the Mitutoyo Corporation Measurement conditions: In accordance with JIS B-0601:2001 (ISO 4287:1997)

Cutoff: 0.8 mm

Evaluation length: 4 mm

Intermediate Layer and Binding Material Evaluation (1)

The Young's modulus of the intermediate layer and the binding material was measured by preparing the following test pieces for evaluation.

A silicone-treated PET film for one-sided peeling with a thickness of 0.5 mm was interposed between a pair of two glass sheets with a thickness of 2 mm, and the composition for intermediate layer formation was held and sandwiched in a 2 mm gap. After the composition was cured by irradiating the composition with ultraviolet rays from both sides of the glass surfaces, the same heat treatment as in the production of the polishing sheet was performed to obtain a sheet-like cured product. The obtained sheet-like cured product was processed into a prescribed size with a diamond cutter to obtain a test piece for intermediate layer evaluation.

In addition, the same process was performed on a composition prepared by excluding the abrasive grains from the composition for three-dimensional element formation to obtain a sheet-like cured product. The obtained sheet-like cured product was processed into a prescribed size with a diamond cutter to obtain a test piece for binding material evaluation.

The Young's modulus of the intermediate layer and the Young's modulus of the binding material were determined using the test piece for intermediate layer evaluation and the test piece for binding material evaluation. The results are shown in Table 1.

TABLE 1 EXAMPLE EXAMPLE EXAMPLE EXAMPLE A-1 A-2 A-3 A-4 YOUNG'S INTERMEDIATE 8.3 × 10⁷ 1.4 × 10⁸ 3.6 × 10⁸ 8.3 × 10⁷ MODULUS LAYER (25° C.) (Pa) BINDING 5.0 × 10⁹ 5.0 × 10⁹ 5.0 × 10⁹ 5.0 × 10⁹ MATERIAL CUT AMOUNT (mg/min) 35.8 33.1 39.8 44.5 Ra (μm) 0.040 0.045 0.050 0.051

TABLE 2 COMPARATIVE COMPARATIVE COMPARATIVE EXAMPLE X-1 EXAMPLE X-2 EXAMPLE X-3 YOUNG'S INTERMEDIATE 3.5 × 10⁹ 2.7 × 10⁹ 3.5 × 10⁹ MODULUS LAYER (25° C.) (Pa) BINDING 5.0 × 10⁹ 5.0 × 10⁹ 5.0 × 10⁹ MATERIAL CUT AMOUNT (mg/min) 51.7 45.5 83.2 Ra (μm) 0.077 0.055 0.118

In a comparison of Examples A-1 to A-3 and Comparative Examples X-1 and X-2, it was possible in Examples A-1 to A-3 to form a smooth surface with a small Ra while maintaining a sufficient cut amount (for example, not less than 30 mg/min). In addition, in a comparison of Example A-4 and Comparative Example X-3, although the cut amount was reduced in Example A-4, Ra became very small, and it was possible to form a smooth surface with even less unevenness.

Example B-1

Preparation of Composition (c-1) for Three-Dimensional Element Formation

A composition (c-1) for three-dimensional element formation was prepared using an acrylic monomer containing a specific polyfunctional monomer.

Specifically, the composition (c-1) for three-dimensional element formation was prepared by mixing 100 parts by mass of tris(2-hydroxyethyl)isocyanurate triacrylate (SR368, available from Arkema), 1.8 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins), 3 parts by mass of a silane coupling agent (KBM-503, 3-(methacryloyloxy)propyl trimethoxysilane, available from Shin-Etsu Chemical Co., Ltd. (Chiyoda-ku, Tokyo)), 293 parts by mass of diamond abrasive grains (average particle size: 15 μm), and 176 parts by mass of propylene glycol methyl ether.

Composition (d-1) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared using CN991 (available from Arkema) as a urethane acrylate.

Specifically, the composition (d-1) for intermediate layer formation was prepared by mixing 78.43 parts by mass of CN991, 19.61 parts by mass of tetrahydrofurfuryl acrylate, and 1.96 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins).

Substrate

A PET film (thickness: 75 μm, Young's modulus at 25° C.: 4×10⁹ Pa) was prepared as a substrate.

Production of Polishing Sheet

A polypropylene molded sheet having concave portions corresponding to the three-dimensional shape illustrated in FIG. 3A was prepared. The composition (c-1) for three-dimensional element formation was applied to the top of the molded film with a bar coater, and the concave portions of the molded film were filled with the composition (c-1) and dried for 3 minutes at 75° C.

Next, the composition (d-1) for intermediate layer formation was applied to the top of the molded film, and a transparent polyester film with a thickness of 75 μm was layered as a substrate and laminated by applying pressure with a roller. Ultraviolet rays were irradiated from the polyester film side, and the molded film was then peeled and heated for 24 hours at 70° C. to obtain a polishing sheet.

Example B-2

Preparation of Composition (c-2) for Three-Dimensional Element Formation

A composition (c-2) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 100 parts by mass of a mixture of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate (ARONIX M-313, diacrylate form content: 30 to 40 mass %, available from Toagosei Co., Ltd. (Minato-ku, Tokyo)) was used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-2) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-3

Preparation of Composition (c-3) for Three-Dimensional Element Formation

A composition (c-3) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 70 parts by mass of a mixture of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate (ARONIX M-313, diacrylate form content: 30 to 40 mass %, available from Toagosei Co., Ltd.) and 30 parts by mass of isocyanurate-based triacrylate (NK ESTER A9300-1CL) were used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-3) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-4

Preparation of Composition (c-4) for Three-Dimensional Element Formation

A composition (c-4) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 90 parts by mass of a mixture of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate (ARONIX M-313, diacrylate form content: 30-40 mass %, available from Toagosei Co., Ltd.) and 10 parts by mass of isobornyl acrylate were used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-4) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-5

Preparation of Composition (c-5) for Three-Dimensional Element Formation

A composition (c-5) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 70 parts by mass of a mixture of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate (ARONIX M-313 (diacrylate form content: 30 to 40 mass %), available from Toagosei Co., Ltd.) and 30 parts by mass of isobornyl acrylate were used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-5) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-6

Preparation of Composition (c-6) for Three-Dimensional Element Formation

A composition (c-6) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 100 parts by mass of SR368D (mixture of trimethylolpropane triacrylate: tris(2-hydroxyethyl)isocyanurate triacrylate=70:30 (mass ratio), available from Arkema) was used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-6) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-7

Preparation of Composition (c-7) for Three-Dimensional Element Formation

A composition (c-7) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 40 parts by mass of trimethylolpropane triacrylate (SR351, available from Arkema) and 60 parts by mass of 2-phenoxyethyl acrylate (SR339, available from Arkema) used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-7) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-8

Preparation of Composition (c-8) for Three-Dimensional Element Formation

A composition (c-8) for three-dimensional element formation was prepared in the same manner as in Example B-1 with the exception that 100 parts by mass of an isocyanurate-based triacrylate (NK ESTER A9300-1CL, available from Shin-Nakamura Chemical Co., Ltd. (Wakayama-shi, Wakayama)) was used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (c-8) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example B-9

Composition (d-2) for Intermediate Layer Formation

A composition for intermediate layer formation was prepared without using a urethane acrylate.

Specifically, the composition (d-2) for intermediate layer formation was prepared by mixing 36.55 parts by mass of isobornyl acrylate, 21.69 parts by mass of trimethylolpropane triacrylate (SR351S, available from Arkema), 36.15 parts by mass of YDCN-700-10, 1.60 parts by mass of a photopolymerization initiator (Omnirad 907, available from IGM Resins), and 4.01 parts by mass of an epoxy resin curing agent (2-ethyl-4-ethylimidazole).

Production of Polishing Sheet

A polypropylene molded sheet having concave portions corresponding to the three-dimensional shape illustrated in FIG. 3A was prepared. The composition (c-3) for three-dimensional element formation was applied to the top of the molded film with a bar coater, and the concave portions of the molded film were filled with the composition (c-3) and dried for 3 minutes at 75° C.

Next, the composition (d-2) for intermediate layer formation was applied to the top of the molded film, and a transparent polyester film with a thickness of 75 μm was layered as a substrate and laminated by applying pressure with a roller. The film was irradiated with ultraviolet rays from the polyester film side. Next, the film was heated for 24 hours at 70° C. to obtain a polishing sheet.

Example B-10 Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-9 with the exception that the composition (c-4) for three-dimensional element formation was used instead of the composition (c-3) for three-dimensional element formation.

Example B-11 Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-9 with the exception that the composition (c-5) for three-dimensional element formation was used instead of the composition (c-3) for three-dimensional element formation.

Polishing Sheet Evaluation (2)

The polishing sheets produced in the examples and the comparative examples were subjected to polishing tests under the following conditions (2), and the cut amount and the surface roughness Ra of the polished surface after 30 seconds were determined. The results are shown in Tables 3, 4, and 5.

Polishing Test Conditions (2)

Polished object: S45C subjected to high-frequency hardening at a hardness of HRC55

Polished object size: 10 mm (Φ)×200 mm (length)

Polishing device: Super Finisher (available from Matsuda Seiki Co., Ltd.)

Revolution speed: 825 rpm

Film feeding: none

Oscillation speed: 1000 rpm

Grinding fluid: 2% aqueous solution of Cimtech 500 (available from CIMCOOL FLUIDS TECHNOLOGY)

Backup roller hardness: Shore A 30°

Notch depth: 4.2 mm

Polishing time: 30 sec

Cut amount: The reduction in the weight of the object to be polished after the polishing test was used as the cut amount.

Average surface roughness Ra: Measured with the following device/conditions.

Device: SURFTEST SV-3100H4 available from the Mitutoyo Corporation

Measurement conditions: In accordance with JIS B-0601:2001 (ISO 4287:1997)

Cutoff: 0.8 mm

Evaluation length: 4 mm

Intermediate Layer and Binding Material Evaluation (2)

The Young's modulus of the intermediate layer and the Young's modulus and compressive yield stress of the binding material were measured by preparing the following test pieces for evaluation.

A silicone-treated PET film for one-sided peeling with a thickness of 0.5 mm was interposed between a pair of two glass sheets with a thickness of 2 mm, and the composition for intermediate layer formation was held and sandwiched in a 2 mm gap. After the composition was cured by irradiating the composition with ultraviolet rays from both sides of the glass surfaces, the same heat treatment as in the production of the polishing sheet was performed to obtain a sheet-like cured product. The obtained sheet-like cured product was processed into a prescribed size with a diamond cutter to obtain a test piece for intermediate layer evaluation.

In addition, the same process was performed on a composition prepared by excluding the abrasive grains from the composition for three-dimensional element formation to obtain a sheet-like cured product. The obtained sheet-like cured product was processed into a prescribed size with a diamond cutter to obtain a test piece for binding material evaluation.

The Young's modulus of the intermediate layer and the Young's modulus and compressive yield stress of the binding material were determined using the test piece for intermediate layer evaluation and the test piece for binding material evaluation. The results are shown in Tables 3, 4, and 5.

Note that in Tables 3 to 5, the “monomer A amount” refers to the content (mass %) of tris(2-hydroxyethyl)isocyanurate triacrylate or tris(2-hydroxyethyl)isocyanurate diacrylate with respect to the total amount of acrylic monomers in the composition for three-dimensional element formation. In addition, the “compressive yield stress” refers to the compressive yield stress (MPa) of the binding material in each polishing sheet.

TABLE 3 EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE B-1 B-2 B-3 B-4 B-5 YOUNG'S INTERMEDIATE 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ MODULUS LAYER (25° C.) (Pa) BINDING 5.2 × 10⁹ 5.4 × 10⁹ 4.4 × 10⁹ 4.8 × 10⁹ 4.1 × 10⁹ MATERIAL MONOMER (A) AMOUNT (%) 100 100 70 90 70 COMPRESSIVE YIELD 174 197 157 164 137 STRESS (MPa) CUT AMOUNT (mg/30 sec) 22 21.6 16.4 16.8 18.1 Ra (μm) 0.04 0.0389 0.0331 0.0312 0.033

TABLE 4 EXAMPLE EXAMPLE EXAMPLE B-6 B-7 B-8 YOUNG'S INTERMEDIATE 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ MODULUS LAYER (25° C.) (Pa) BINDING 4.6 × 10⁹ 3.7 × 10⁹ 3.3 × 10⁹ MATERIAL MONOMER (A) AMOUNT (%) 30 0 0 COMPRESSIVE YIELD 123 83 109 STRESS (MPa) CUT AMOUNT (mg/30 sec) 13.2 7.4 12.9 Ra (μm) 0.0217 0.0243 0.0384

TABLE 5 EXAMPLE EXAMPLE EXAMPLE B-9 B-10 B-11 YOUNG'S INTERMEDIATE 3.5 × 10⁹ 3.5 × 10⁹ 3.5 × 10⁹ MODULUS LAYER (25° C.) (Pa) BINDING 4.4 × 10⁹ 4.8 × 10⁹ 4.1 × 10⁹ MATERIAL MONOMER (A) AMOUNT (%) 70 90 70 COMPRESSIVE YIELD 157 164 137 STRESS (MPa) CUT AMOUNT (mg/30 sec) 15.5 18.3 18.2 Ra (μm) 0.0434 0.0412 0.0568

In Examples B-6 to B-8, it was possible to form a smooth surface with a smaller Ra than in Examples B-9 to B-11 by using an intermediate layer with a Young's modulus within a prescribed range. In addition, in Examples B-9 to B-11, a binding material with a higher compressive yield stress than in Examples B-6 to B-8 was formed by using a specific polyfunctional monomer, and a higher cut amount was realized. Further, in Examples B-1 to B-5, it was possible to achieve both a high cut rate and a small Ra by using an intermediate layer with a Young's modulus within a prescribed range and forming three-dimensional elements using a specific polyfunctional monomer.

Example C-1

Preparation of Composition (e-1) for Three-Dimensional Element Formation

A composition (e-1) for three-dimensional element formation was prepared using an acrylic monomer containing a specific polyfunctional monomer.

Specifically, the composition (e-1) for three-dimensional element formation was prepared by mixing 100 parts by mass of tris(2-hydroxyethyl)isocyanurate triacrylate (SR368, available from Arkema), 1.8 parts by mass of a photopolymerization initiator (Omnirad 369, available from IGM Resins), 4.4 parts by mass of a silane coupling agent (KBM-503, 3-(methacryloyloxy)propyl trimethoxysilane, available from Shin-Etsu Chemical Co., Ltd.), 443 parts by mass of alumina abrasive grains (WA#800, available from Fujimi Incorporated (Kiyosu-shi, Aichi), and 176 parts by mass of propylene glycol methyl ether.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example B-1 with the exception that the composition (e-1) for three-dimensional element formation was used instead of the composition (c-1) for three-dimensional element formation.

Example C-2

Preparation of Composition (e-2) for Three-Dimensional Element Formation

A composition (e-2) for three-dimensional element formation was prepared in the same manner as in Example C-1 with the exception that 100 parts by mass of a heavy calcium carbonate filler (Escaron #800), available from Sankyo Seifun Co., Ltd. (Niimi-shi, Okayama) was further mixed as a filler.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example C-1 with the exception that the composition (e-2) for three-dimensional element formation was used instead of the composition (e-1) for three-dimensional element formation.

Example C-3

Preparation of Composition (e-3) for Three-Dimensional Element Formation

A composition (e-3) for three-dimensional element formation was prepared in the same manner as in Example C-1 with the exception that 100 parts by mass of a mixture of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate (ARONIX M-313, diacrylate form content: 30 to 40 mass %, available from Toagosei Co., Ltd.) was used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example C-1 with the exception that the composition (e-3) for three-dimensional element formation was used instead of the composition (e-1) for three-dimensional element formation.

Example C-4

Preparation of Composition (e-4) for Three-Dimensional Element Formation

A composition (e-4) for three-dimensional element formation was prepared in the same manner as in Example C-1 with the exception that 100 parts by mass of SR368D (mixture of trimethylolpropane triacrylate: tris(2-hydroxyethyl)isocyanurate triacrylate=70:30 (mass ratio), available from Arkema) was used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example C-1 with the exception that the composition (e-4) for three-dimensional element formation was used instead of the composition (e-1) for three-dimensional element formation.

Example C-5

Preparation of Composition (e-5) for Three-Dimensional Element Formation

A composition (e-5) for three-dimensional element formation was prepared in the same manner as in Example C-1 with the exception that 40 parts by mass of trimethylolpropane triacrylate (SR351, available from Arkema) and 60 parts by mass of 2-phenoxyethyl acrylate (SR339, available from Arkema) used instead of tris(2-hydroxyethyl)isocyanurate triacrylate.

Production of Polishing Sheet

A polishing sheet was produced in the same manner as in Example C-1 with the exception that the composition (e-5) for three-dimensional element formation was used instead of the composition (e-1) for three-dimensional element formation.

The cut amount and the surface roughness Ra of the polished surface after 30 seconds were determined for the polishing sheets produced in the examples and the comparative examples using the same methods as in the polishing sheet evaluation (2) described above. The results are shown in Table 6.

In addition, a test piece for evaluation was produced with the same method as in the intermediate layer and binding material evaluation (2) described above, and the Young's modulus of the intermediate layer and the Young's modulus and compressive yield stress of the binding material were determined. The results are shown in Table 6.

Note that in Table 6, the “monomer A amount” refers to the content (mass %) of tris(2-hydroxyethyl)isocyanurate triacrylate or tris(2-hydroxyethyl)isocyanurate diacrylate with respect to the total amount of acrylic monomers in the composition for three-dimensional element formation. In addition, the “compressive yield stress” refers to the compressive yield stress (MPa) of the binding material in each polishing sheet.

TABLE 6 EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE C-1 C-2 C-3 C-4 C-5 YOUNG'S INTERMEDIATE 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ 8.3 × 10⁷ MODULUS LAYER (25° C.) (Pa) BINDING 5.2 × 10⁹ 10.3 × 10⁹ 5.4 × 10⁹ 4.6 × 10⁹ 3.7 × 10⁹ MATERIAL MONOMER (A) AMOUNT (%) 100 100 100 30 0 COMPRESSIVE YIELD 174 201 197 123 83 STRESS (MPa) CUT AMOUNT (mg/30 sec) 7.8 9.5 8.8 4.7 5.5 Ra (μm) 0.0448 0.0398 0.0422 0.0449 0.0622

In Examples C-1 to C-5, it was possible to form a smooth surface with a small Ra using alumina abrasive grains. In addition, in Examples C-1 to C-3, in particular, a binding material with a higher compressive yield stress than in Examples C-4 and C-5 was formed by using a specific polyfunctional monomer, and a higher cut amount was realized.

REFERENCE NUMERALS

10, 20: Polishing sheet; 11, 21: Substrate; 12, 22: Three-dimensional element; 13, 23: Intermediate layer; 121, 122, 123, 124: Three-dimensional part 

1. A polishing sheet comprising: a substrate; a plurality of three-dimensional elements containing abrasive grains and a binding material; and an intermediate layer provided between the three-dimensional elements and the substrate so as to join the substrate and the three-dimensional elements, wherein a Young's modulus of the substrate at 25° C. is not less than 3.0×10⁹ Pa; and a Young's modulus of the intermediate layer at 25° C. is not less than 1.0×10′ Pa and not greater than 5.0×10⁸ Pa.
 2. The polishing sheet according to claim 1, wherein a Young's modulus of the binding material at 25° C. is not less than 1.0×10⁹ Pa.
 3. The polishing sheet according to claim 1, wherein the binding material contains: a resin composition containing an acrylic monomer; and not less than 60 mass % of the acrylic monomer is a polyfunctional monomer selected from the group consisting of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate.
 4. The polishing sheet according to claim 1, wherein a breaking elongation of the substrate is not greater than 200%.
 5. The polishing sheet according to claim 1, wherein the substrate contains at least one selected from the group consisting of resin films and metal films.
 6. The polishing sheet according to claim 1, wherein the intermediate layer contains a cured product of a resin composition containing a urethane acrylate.
 7. The polishing sheet according to claim 1, wherein the binding material contains a phenol resin.
 8. A polishing sheet comprising: a substrate; a plurality of three-dimensional elements containing abrasive grains and a binding material; and an intermediate layer provided between the three-dimensional elements and the substrate so as to join the substrate and the three-dimensional elements, wherein the binding material contains a cured product of a resin composition containing an acrylic monomer; and not less than 60 mass % of the acrylic monomer is a polyfunctional monomer selected from the group consisting of tris(2-hydroxyethyl)isocyanurate triacrylate and tris(2-hydroxyethyl)isocyanurate diacrylate.
 9. A polishing method using the polishing sheet according to claim 1, the method comprising sliding the polishing sheet and an object to be polished while pressing the polishing sheet against the object to be polished under a load of not less than 1.0×10⁶ Pa.
 10. A polishing method using the polishing sheet according to claim 8, the method comprising sliding the polishing sheet and an object to be polished while pressing the polishing sheet against the object to be polished under a load of not less than 1.0×10⁶ Pa. 